Here is a little bit of GMing philosophy - when you play in my game, I am on your side. I really hope that you do well. I just won't do anything to ensure that you do well. Want to attempt something unusual? I will entertain what seem to be reasonable arguments. I will assign what seems like a fair chance, to me. The odds are good that, if I make a ruling, that ruling is skewed in the players' favour.
But the dice still fall where they may, and I will fudge neither rolls nor statistics nor monster behaviour to ensure either your success or your survival. I want you to succeed - I really do - but I want you to succeed in a meaningful way. That means giving your opponents the brains that they should have, and it means allowing bad things to happen as well as good. That means allowing a TPK to happen. And happen again. And happen again after that. Unless you do something to make it not happen.
When I brought this up on DragonsFoot, I was told that this was smoke and mirrors - the GM cannot both be on the players' side and act as an impartial referee. Let me rephrase that, because what I am saying is that the GM can be on the players' side and still understand the importance of refereeing impartially. Just as a player can advocate for his character fairly, without cheating. Hoping for a good outcome does not mean you screw the game in order to ensure it occurs.
If I was acting against the players, or even creating a completely impartial scenario, it would be all too easy to create situations where TPKs were inescapable. I would have a thick folder filled with the dead, and no players at the table, because, really, what would be the point? Even a "killer" dungeon like Death Frost Doom or The Tomb of Horrors is more player-friendly than a similar situation would "realistically" be.
And I play games with people I like. I feel for them when they lose a beloved character. I am happy for them when they succeed beyond hope.
I am on their side.
But I won't do anything to make them win. And the dice may not be.
And it is not always obvious to the players that I am on their side, either. It's fun when the going gets tough, and I am grinning like a hyena waiting for a wildebeest to fall. Even though I hope they find a way out, I relish the tight spot for what it is.
These are not contradictory positions to take. Any player worth his salt relishes the dangerous moments as well. Although she might not be able to focus on her enjoyment of those moments at the time (being busy with trying to find a way to survive, or mourning the loss of a character), but those are the moments that are relived through gamer chatter days, months, and years later.
A good GM is on the side of the players, and wants them to do well and have fun, but is not on the side of the characters. A good GM knows that pulling punches removes the value of choice from the players, just as a good GM ensures that context is available for choices, but doesn't force context on the players if they choose to ignore it/not look for it. A good GM allows the players to make choices, and allows the characters to live or die by the quality of those choices.
A GM who punishes characters when the players make good choices, or coddles the characters when the players make poor choices, is undesirable. Both remove the greatest value that the tabletop game offers over other forms of entertainment.
Some players may think they want easy victories, or even guaranteed victories, but handing crap like that out is not what someone on your side does.
Call it tough love.